1. Field of the Invention
This invention relates to a wear resistant iron base alloy containing large amount of stable residual austenite to improve wear resistance as engine valve seat inserts (VSI). The inventive alloy is especially useful to make intake valve seat inserts used in heavy duty internal combustion engines where the working temperature is not high enough to form high oxidizing atmosphere to promote the formation of protective oxides on the surfaces of VSI's. In a further aspect, this invention relates to components made from such alloys, either cast or hardfaced. Alternatively, components made of such alloys may be made by conventional powder metallurgy methods either by cold pressing and sintering or by hot pressing at elevated pressures for wear resistant applications.
2. Background Art
Wear resistance and wear compatibility with common valve alloys are important properties for intake valve seat insert alloys used in internal combustion engines, where the average intake VSI working temperature is around 400-650° F. and wear compatibility is defined as the tendency to damage the mating valve or valve facing alloys. Currently, iron base and cobalt base alloys are commonly used for intake valve seat inserts in diesel or dry fuel internal combustion engines. Because of the low cost, iron base alloys, like high chromium iron base alloys and high speed tool steel type alloys, are widely used as intake VSI materials in engines with medium or light loading conditions. Large amount of alloy carbides and hard martensite matrix are the essential factors for good wear resistance of these iron base alloys. However, these alloys can not provide enough wear resistance or wear compatibility in many new internal combustion engines with higher power output and less emission. Although cobalt base alloys like Stellite® 3 or Tribaloy® T-400 can offer enough wear resistance as intake VSI materials in certain demanding applications, the high cost of cobalt element limits these cobalt base alloys to be widely accepted in the engine industry.
There are also many tool steels or other iron base alloy patents for wear resistant applications. U.S. Pat. No. 4,778,522, U.S. Pat. No. 4,155,754, U.S. Pat. No. 4,844,024, are a few examples of tool steel type wear resistant alloys.
U.S. Pat. No. 4,021,205 discloses a sintered powdered ferrous alloy article, in which carbon is 1.0-4.0%, chromium 10.0-30.0 wt %, nickel 2.0-15.0%, molybdenum 10.0-30.0%, cobalt 20.0-40.0%, niobium 1.0-5.0%, and the balance being iron.
U.S. Pat. No. 6,248,292 discloses an iron base overlaying alloy for internal combustion valves. This alloy contains carbon 0.5-3.0%, molybdenum 20.0-70.0%, nickel 5.0-40.0%, and the balance being Fe. In conditions where oxides are easily formed, the overlaying alloy has the following composition: carbon 0.5-3.0%, chromium 0.1-10.0%, molybdenum 20.0-60.0%, nickel 5.0-40.0%, and the balance being iron and unavoidable impurities.
Japanese Patent Publication 59-229465 discloses an iron base alloy with excellent wear resistance by incorporating a specific ratio of C, Cr, Nb, Mo, W, V and Ta in Fe. This alloy contains carbon 1.0-3.0%, chromium 10.1-20.0%, niobium 0.2-5.0%, one or two kinds among molybdenum 0.5-10.0%, tungsten 0.5-10.0%, vanadium 0.5-5.0%, tantalum 0.2-5.0%.
U.S. Pat. No. 5,316,596 discloses a roll shell steel with carbon 1.5-3.5%, silicon 1.5% or less, manganese 1.2% or less, chromium 5.5-12.0%, molybdenum 2.0-8.0%, niobium 0.6-7.0% vanadium 3.0-10.0%, and satisfies the formulae: V+1.8Nb<7.5C-6.0%, 0.2<Nb/V<0.8, and remainder of Fe and inherent impurities.
U.S. Pat. No. 5,578,773 discloses a powder metallurgy high speed steel with carbon 2.2-2.7%, silicon 1.0% or less, manganese from trace to 1.0%, chromium 3.5-4.5%, molybdenum 2.5-4.5%, tungsten 2.5-4.5%, vanadium 7.5-9.5%, and remainder of Fe and inherent impurities.
It is an object of this invention to develop an iron base alloy with improved wear compatibility and wear resistance for VSI application.